Field
Aspects of the present invention generally relate to an inkjet recording apparatus provided with a sub tank disposed between a recording head and an ink tank.
Description of the Related Art
Inkjet recording apparatuses provided with a sub tank have been used widely. Japanese Patent Laid-Open No. 2013-184424, for example, discloses an inkjet recording apparatus provided with a sub tank.
As illustrated in FIG. 9, the inkjet recording apparatus disclosed in Japanese Patent Laid-Open No. 2013-184424 is provided with a sub tank 400 disposed below an ink tank 500 in the vertical direction. The sub tank 400 and a recording head 100 communicate with each other via a supply tube 200. The ink tank 500 and the sub tank 400 communicate with each other via a hollow pipe 800 formed by a metal needle.
The inkjet recording apparatus disclosed in Japanese Patent Laid-Open No. 2013-184424 is further provided with an ink reservoir 300 of which volume is variable. The ink reservoir 300 is formed by a flexible member and is located between the sub tank 400 and the supply tube 200. As the ink reservoir 300 increases in volume, ink in the ink tank 500 is drawn into the sub tank 400, and as the ink reservoir 300 decreases in volume, air in the sub tank 400 is pushed out to the ink tank 500.
In the inkjet recording apparatus disclosed in Japanese Patent Laid-Open No. 2013-184424, a metal solid pipe 808 is provided on a top panel of the sub tank 400. Whether the sub tank 400 is filled with ink is determined by a resistance value when a weak current is made to flow between the solid pipe 808 and the hollow pipe 800. A lower end 809 of the solid pipe 808 is disposed lower than a lower end 807 of the hollow pipe 800.
That is, when both the lower end 807 of the hollow pipe 800 (an electrode) and the lower end 809 of the solid pipe 808 (an electrode) are in contact with a liquid surface in the sub tank 400 (i.e., when the sub tank 400 is in a full state), the resistance value between the electrodes (800 and 808) decreases. When the lower end (807 or 809) of the electrode (800 and 808) is not in contact with the liquid surface (i.e., when the sub tank 400 is not a full state), the resistance value between the electrodes (800 and 808) increases. Therefore, whether the sub tank 400 is filled with ink may be estimated (determined) based also on variation of the resistance value between the hollow pipe 800 (the electrode) and the solid pipe 808 (the electrode).
In the inkjet recording apparatus disclosed in Japanese Patent Laid-Open No. 2013-184424, as illustrated in FIG. 9, when the ink is supplied to the sub tank 400 from the ink tank 500 through the hollow pipe 800, the ink may drip at the lower end 807 of the hollow pipe 800 (a “liquid column” phenomenon). When an ink dripping portion (D) is brought into contact with the liquid surface, electrical resistance between the hollow pipe 800 (the electrode) and the solid pipe 808 (the electrode) decreases. Therefore, the electrical resistance between the electrodes (800 and 808) changes (decreases) while the liquid surface in the sub tank 400 has not actually risen up to the position of the lower end 807 of the hollow pipe 800. As a result, it may be wrongly detected that the sub tank 400 has been filled with ink (a full state).
Especially during the drawing of the ink in the sub tank 400 from the ink tank 500 by the ink reservoir 300, the ink dripping portion (D) is easy to appear and such wrong detection is easy to be conducted. Therefore, in the inkjet recording apparatus disclosed in Japanese Patent Laid-Open No. 2013-184424, the ink amount stored in the sub tank 400 cannot always be detected correctly.